The electronics, display and energy industries rely on the formation of coatings and patterns of conductive and other electronically active materials to form circuits on organic and inorganic substrates. The primary methods for generating these patterns are screen printing for features larger than about 100 μm and thin film and etching methods for features smaller than about 100 μm. Other subtractive methods to attain fine feature sizes include the use of photo-patternable pastes and laser trimming.
It is the trend in the electronics industry to make smaller and less expensive electronic devices that provide higher resolution and enhanced display performance. As a result, it has become necessary to develop new materials and new approaches to manufacture such devices.
At times it will be preferable to coat an entire substrate with a surface layer and then, in a subtractive process, etch away the undesired portions of the surface layer to form the image. On the nano-scale, this is one of the fundamental underlying processes of the semiconductor industry. The technology is aggressive and well suited to small devices but there are many instances where the resolution of the semiconductor industry is not required. For example, in the photovoltaic industry, it is often required that long straight lines be selectively cut into devices. This is often done by laser scribing, which can be difficult when the layer to be removed is transparent and the layer below it to be left is opaque.
A technique to selectively etch portions of one layer while not damaging the subsequent underlayer is desirable for a wide variety of applications. This may be accomplished through the use of selective etchants that react chemically to remove one layer while leaving the next layer of differing composition undisturbed. The portions of the pattern to be retained are first covered with a resist. The etching process is carried out by exposing the entire area to the etchant. When the etching process is complete, the resist must be removed. A method that does not require the patterning and subsequent removal of a resist layer would be advantageous in certain applications.
Ink jet techniques allow the selective deposition of low viscosity, fluid materials onto a substrate surface. Because of the small droplet size of ink jet printing, it can be difficult to apply appreciable quantities of material, though this can be done utilizing multiple passes over the same area of an image. Appreciable drying time between passes may be required to prevent flowing of the image so that resolution is not compromised.
In solution spinning, a concentrated solution of a polymer is forced through a spinneret. The face of the spinneret is in contact only with a fluid, which is usually air. Because solvent evaporation is generally a slow process, after traveling a short distance through the air, typically 0.1-10 cm., the concentrated solution (in the form of a fine “jet”) usually enters a coagulant, which extracts the solvent from the polymer, resulting in the formation of a polymer fiber. The coagulant is frequently water or, as in the case of the process disclosed herein, air. Importantly, in the gap between the spinneret face and the coagulant, the polymer solution, which is usually quite viscous and somewhat viscoelastic, is drawn, resulting in a smaller diameter jet of polymer solution entering the coagulant than was extruded from the spinneret holes. The amount of drawing that can be done is limited, because above some maximum draw value the fibers tend to break. This technique may be extended to processes for the selective deposition of materials as disclosed in US Patent application US2005/0089679 A1.
Despite the advances in such systems, the multiple, time-intensive steps required for current etching techniques employing resists are a limitation to manufacturing. Manufacturers are continuously seeking improved techniques and compositions that can fulfill their needs for selective materials removal. The techniques may be used in very specific applications if they provide greater speed and more specific materials removal. Such materials can increase the speed of the manufacturing processes without compromising high resolutions in the lines and spaces of the circuit or display patterns. The present invention is directed to such processes, materials and compositions suitable for implementation of the processes, and methods for production of the materials.